Method and assembly of an electric machine

ABSTRACT

A method and assembly of a dry cavity oil cooled electric machine includes a housing, a shaft configured to operably couple with a source of rotational force and rotate about a rotational axis, and an exciter rotor and a permanent magnet generator rotor carried by the shaft, wherein the exciter rotor and the permanent magnet generator rotor rotate relative to the housing, which provides such a construction of dry cavity generators that have high efficiency and high power density.

BACKGROUND OF THE INVENTION

Contemporary aircraft engines include electric machine assemblies, orgenerator systems, which utilize a running aircraft engine in agenerator mode to provide electrical energy to power systems andcomponents on the aircraft. Some aircraft engines can further includestarter/generator (S/G) systems or motor/generator (M/G), which act as amotor to start an aircraft engine from its high pressure spool or amotor to drive the engine from its low pressure spool, and as agenerator to provide electrical energy to power systems on the aircraftafter the engine is running. Motors and generators can be wet cavitysystems, wherein a cavity housing the rotor and stator is exposed toliquid coolant, or dry cavity systems, wherein the cavity is not exposedto liquid coolant. Dry cavity cooling can also utilize liquid coolant inone or more contained cooling systems, but they are still considered drycavity so long as the cavity is not exposed to liquid coolant. Ingeneral, dry cavity systems generally have less losses, higherefficiency, higher reliability, less required maintenance, and attitudeindependence over wet cavity systems. In contrast, the power density ofa wet cavity electric machine can be higher than that of a dry cavityelectric machine due to its higher cooling effectiveness. However, thismay not be true once more than one contained cooling systems applied ina dry cavity machine.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the disclosure relates to an electric machine assemblyincluding a housing, a shaft configured to operably couple with a sourceof rotational force and rotate about a rotational axis, and an exciterrotor and a permanent magnet generator rotor carried by the shaft. Theexciter rotor and the permanent magnet generator rotor are substantiallycoplanar at a plane orthogonal to the rotational.

In another aspect, the disclosure relates to a method of operating anelectric machine including rotating a rotatable shaft about a rotationalaxis, the shaft carrying an arm extending radially outward from theshaft, an exciter rotor, and a permanent magnet generator rotor, whereinat least one of the exciter rotor or the permanent magnet generatorrotor is mounted to the arm, and wherein the exciter rotor and thepermanent magnet generator rotor are substantially coplanar at a planeorthogonal to the rotational axis.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of a gas turbine engine having a generatorin accordance with various aspects described herein.

FIG. 2 is a perspective view of an exterior of the generator of FIG. 1,in accordance with various aspects described herein.

FIG. 3 is a schematic cross-sectional view of the generator, taken alongline of FIG. 2 and illustrating the structure of the generator, inaccordance with various aspects described herein.

FIG. 4 is a schematic zoomed view of the generator of FIG. 3, inaccordance with various aspects described herein.

FIG. 5 is a schematic cross-sectional view of the generator,illustrating the cooling system of the generator, in accordance withvarious aspects described herein.

FIG. 6 is a schematic cross-sectional view of a stator winding of thegenerator of FIG. 3, in accordance with various aspects describedherein.

FIG. 7 is a schematic view of the stator windings of the generator ofFIG. 3 and a cooling system, in accordance with various aspectsdescribed herein.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Aspects of the disclosure can be implemented in any environment using anelectric generator or motor regardless of whether the electric generatoror motor provides a driving force or generates electricity. For purposesof this description, such an electric motor will be generally referredto as an electric machine, electric machine assembly, generator, orsimilar language, which is meant to clarify that one or morestator/rotor combinations can be included in the machine.

While “a set of” various elements will be described, it will beunderstood that “a set” can include any number of the respectiveelements, including only one element. As used herein, the terms “axial”or “axially” refer to a dimension along a longitudinal axis of anelectric machine or along a longitudinal axis of a component disposedwithin the electric machine. As used herein, the terms “radial” or“radially” refer to a dimension extending between a center longitudinalaxis of the electric machine, an outer rotational circumference, or acircular or annular component disposed within the electric machine. Theuse of the terms “proximal” or “proximally,” either by themselves or inconjunction with the terms “radial” or “radially,” refers to moving in adirection toward the center longitudinal axis, or a component beingrelatively closer to the center longitudinal axis as compared to anothercomponent.

All directional references (e. g., radial, axial, upper, lower, upward,downward, left, right, lateral, front, back, top, bottom, above, below,vertical, horizontal, clockwise, counterclockwise) are only used foridentification purposes to aid the reader's understanding of thedisclosure, and do not create limitations, particularly as to theposition, orientation, or use thereof. Connection references (e. g.,attached, coupled, connected, and joined) are to be construed broadlyand can include intermediate members between a collection of elementsand relative movement between elements unless otherwise indicated. Assuch, connection references do not necessarily infer that two elementsare directly connected and in fixed relation to each other. Theexemplary drawings are for purposes of illustration only and thedimensions, positions, order and relative sizes reflected in thedrawings attached hereto can vary.

While this description is primarily directed toward an electric machineproviding power generation, it is also applicable to an electric machineproviding a driving force or an electric machine providing both adriving force and power generation. Further, while this description isprimarily directed toward an aircraft environment, aspects of thedisclosure are applicable in any environment using an electric machine.Thus, a brief summary of a contemplated environment should aid in a morecomplete understanding.

FIG. 1 illustrates a gas turbine engine 10 having an accessory gear box(AGB) 12 and a generator 14 according to an aspect of the disclosure.The gas turbine engine 10 can be a turbofan engine, such as a GeneralElectric GEnx or CF6 series engine, commonly used in modern commercialand military aviation or it could be a variety of other known gasturbine engines such as a turboprop or turboshaft. The gas turbineengine 10 can also have an afterburner that burns an additional amountof fuel downstream of the low pressure turbine region to increase thevelocity of the exhausted gases, and thereby to increase thrust. The AGB12 can be coupled to a turbine shaft (not shown) of the gas turbineengine 10 by way of a mechanical power take off 16. The gas turbineengine 10 can be any suitable gas turbine engine used in moderncommercial and military aviation or it could be a variety of other knowngas turbine engines such as a turboprop or turboshaft. The type andspecifics of the gas turbine engine 10 are not germane to the disclosureand will not be described further herein. While a generator 14 is shownand described, aspects of the disclosure can include any electricalmachine, generator, motor, starter/generator, of combination there, andare not limited to generator aspects that can provide electrical power.For instance, in one non-limiting example, a generator can operate in apower generation mode to provide power, or in a motor mode, whereinpower is consumed to generate rotational force, such as propulsion.Non-limiting examples of the generator 14 can include synchronousmachine architectures.

FIG. 2 more clearly illustrates the generator 14 and its housing 18.Multiple electrical connections can be provided on the exterior of thegenerator 14 to provide for the transfer of electrical power to and fromthe generator 14. The electrical connections can be further connected bycables to an electrical power distribution node of an aircraft havingthe gas turbine engine 10 to power various items on the aircraft, suchas lights and seat-back monitors.

Non-limiting aspects of the disclosure can be included wherein, forinstance, a clamping interface can be included and used to clamp thegenerator 14 to the AGB 12. In another non-limiting aspect of thedisclosure, the generator 14 can include a liquid coolant system forcooling or dissipating heat generated by components of the generator 14or by components proximate to the generator 14, such as the gas turbineengine 10. For example, the generator 14 can include a liquid coolingsystem using oil as a coolant. The liquid cooling system can include acooling fluid inlet port and a cooling fluid outlet port (not shown) forcontrolling the supply of coolant to the generator 14. In yet anothernon-limiting aspect of the disclosure, the generator 14 can furtherinclude other liquid cooling system components, such as a liquid coolantreservoir fluidly coupled with the cooling fluid inlet port or coolingfluid outlet port, or a liquid coolant pump to forcibly supply thecoolant through the ports or generator 14. Oil is merely onenon-limiting example of a liquid coolant that can be used in aspects ofthe disclosure. Additional or alternative types of fluid coolant can beincluded in aspects of the disclosure, including but not limited to,liquids, gases, fluids, or a combination thereof.

The interior of the generator 14 is best seen in FIG. 3, which is afirst sectional view of the generator 14 shown in FIG. 2. A rotatableshaft 40 is located within the generator 14 and is the primary structurefor supporting a variety of components. The rotatable shaft 40 can havea single diameter or one that can vary along its length. The rotatableshaft 40 is supported by spaced bearings 42 and 44 and configured torotate about axis of rotation 41. Several of the elements of thegenerator 14 have a fixed component and a rotating component, with therotating component being provided on the rotatable shaft 40. Examples ofthese elements can include a main machine 50, housed within a mainmachine cavity 51, an exciter 60, and a permanent magnet generator (PMG)70. The corresponding rotating component comprises a main machine rotor52, an exciter rotor 62, and a PMG rotor 72, respectively, and thecorresponding fixed component comprises a main machine stator 54 orstator core, an exciter stator 64, and a PMG stator 74.

As shown, aspects of the exciter 60, and the PMG 70 can be coplanar to aplane 22 orthogonal or perpendicular to the axis of rotation 41. In thissense, non-limiting aspects of the exciter 60, such as the exciter rotor62 or exciter stator 64, or aspects of the PMG 70, such as the PMG rotor72 or the PMG stator 74 can be coplanar at the orthogonal plane 22. Alsoas shown, the exciter 60, the exciter rotor 62, or the exciter stator 64can be disposed along an outer radius of the PMG 70, the PMG rotor 72,or the PMG stator 74. Thus, the exciter 60 can be located radiallyoutward from the PMG 70, relative to the axis of rotation 41.

While the illustrated aspects of the disclosure are shown wherein theexciter 60 and the PMG 70 components are co-located at the orthogonalplane 22, aspects of the disclosure can be included wherein the exciter60 and the PMG 70 components are substantially coplanar with each other,or with a single orthogonal plane 22. Additional aspects of thedisclosure can be included wherein aspects of the exciter 60 and the PMG70 components are configured, arranged, disposed, or the like in acoplanar relationship wherein at least a portion of the exciter 60 orthe PMG 70 axially overlaps the other component along the axis ofrotation 41. Thus, “substantially coplanar” is not limited to a preciseplanar representation, and can include any overlapping betweenrespective components 60, 70 along an axial segment.

The generator 14 can also include an arm 24 disposed on the rotatableshaft 40 and configured to co-rotate with the shaft 40. The arm 24 canalso provide a mounting for at least one of the PMG rotor 72 or theexciter rotor 62. Non-limiting aspects of the disclosure can be includedwherein another of the PMG rotor 72 or the exciter rotor 62 can berotationally mounted directly to the rotatable shaft 40. In anothernon-limiting aspect of the disclosure both the PMG rotor 72 and theexciter rotor 62 can be rotationally mounted to the arm 24. The arm 24can include a segment 26 extending radially away from the rotatableshaft 40 such that the arm 24 or the segment 26 has a larger radius, asmeasured from the axis of rotation 41, compared with the rotatable shaft40. Non-limiting aspects of the disclosure can be included wherein thearm 24 or segment 26 can include a set of arms 24 or segments 26 thatare radially spaced about the rotatable shaft 40. The set of arms 24 orsegments 26 can be radially spaced based on a desired rotational balancebetween the exciter rotor 62, the PMG rotor 72, permanent magnets, anumber of poles of the exciter rotor 62 or PMG rotor 72, the set of arms24, the set of segments 26, or a combination thereof.

In another non-limiting aspect of the disclosure, the arm 24 or segment26 can include a continuous arm 24 or segment 26, where the arm 24 orsegment 26 extends continuously (e. g. without radial breaks or radialgaps) about the axis of rotation 41. In this non-limiting aspect of thedisclosure, the exciter rotor poles, the PMG rotor poles, or permanentmagnets can be disposed, arranged, radially spaced, or the like based ona desired rotational balance between the exciter rotor 62, the PMG rotor72, permanent magnets, a number of poles of the exciter rotor 62 or PMGrotor 72, the arm 24, the segment 26, or a combination thereof.

While the illustrated example shows aspects of the exciter rotor 62, theexciter stator 64, the PMG rotor 72, and the PMG stator 74 arerepresented in the same cross-sectional view for ease of understanding,aspects of the disclosure can be included wherein the exciter rotor 62,the exciter stator 64, the PMG rotor 72, or the PMG stator 74 areradially offset from other components. For instance, in one non-limitingaspect, the PMG rotor 72 can be radially offset from the exciter rotor62 to reduce, prevent, or eliminate magnetic interference between therespective components. In another non-limiting aspect of the disclosure,aspects of the exciter 60 or PMG 70 can be electromagnetically shieldedfrom corresponding components, such as radially separating the exciter60 from the PMG 70, to reduce, prevent, or eliminate magneticinterference between the respective components.

In this manner, the main machine rotor 52, exciter rotor 62, and PMGrotor 72 are disposed on, or rotationally supported by the rotatableshaft 40, such as directly by the shaft 40, or indirectly by the shaft40, as in the aforementioned arm 24. The fixed components, such as themain machine stator 54, the exciter stator 64, or the PMG stator 74 canbe mounted to any suitable part of the housing 18, such that relativerotation of the rotor components can electromechanically interact withthe respective stator components 54, 64, 74. The main machine stator 54,exciter stator 64, and PMG stator 74 define an interior through whichthe rotatable shaft 40 extends.

It will be understood that the main machine rotor 52, exciter rotor 62,and PMG rotor 72 can have a set of rotor poles, including, but notlimited to two rotor poles, and that the main machine stator 54, exciterstator 64, and PMG stator 74 can have a set of stator teeth or statorpoles, including, but not limited to two stator teeth or stator poles.The set of rotor poles can generate a set of magnetic fields relative tothe set of stator poles, such that the generator 14 can operate throughthe interaction of the magnetic fields and current-carrying conductorsto generate force or electrical power. The exciter 60 can provide directcurrent to the main machine 50 and the main machine 50 and PMG 70 cansupply AC electrical power when the rotatable shaft 40 rotates.

At least one of the rotor poles and stator teeth or stator poles can beformed by a core with a post and wire wound about the post to form awinding, with the winding having at least one end turn. Aspects of thedisclosure shown include at least one set of stator windings 90 arrangedlongitudinally along the stator housing 18, that is, in parallel withhousing 18 and the rotor axis of rotation 41. The set of stator windings90 can also include a set of stator winding end turns 92 extendingaxially beyond opposing ends of a longitudinal length of a main machinestator 54.

The components of the generator 14 can be any combination of knowngenerators. For example, the main machine 50 can be either a synchronousor asynchronous generator. In addition to the accessories shown in thisaspect, there can be other components that need to be operated forparticular applications. For example, in addition to theelectromechanical accessories shown, there can be other accessoriesdriven from the same rotatable shaft 40 such as the liquid coolant pump,a fluid compressor, or a hydraulic pump.

FIG. 4 illustrates a zoomed view of the generator 14 for betterunderstanding of the operation and effect of the substantially coplanarexciter 60 and PMG 70, for ease of understanding.

By arranging, disposing, locating, or the like, aspects of the exciter60 and PMG 70 about a substantially coplanar relationship, such as aboutplane 22 or section along the axial direction of the rotational axis 41,the overall length of the rotatable shaft 40 can be reduced, comparedwith a generator, electrical machine, or the like wherein the exciter 60and PMG 70 are arranged in series or sequentially along the axialdirection of the rotational axis. By reducing the overall length of therotatable shaft 40, the structure of the generator 14 can be reduced, asmeasured in volume, length, size, compactness, displacement, or thelike. In this sense, reducing the size of the generator 14 increases thepower density of the generator 14, compared with similarly situatedelectrical machine where the exciter 60 and PMG 70 are arranged inseries or sequentially along the axial direction of the rotational axis.

As explained above, the generator 14 can be oil cooled and thus caninclude a cooling system. The cooling oil can be used to dissipate heatgenerated by the electrical and mechanical functions of the generator14. FIG. 5 illustrates a non-limiting example cooling system 80. FIG. 5illustrates a second sectional view, different from the sectional viewof FIG. 3, to better illustrate aspects of the cooling system 80. In oneexample, aspects of the cooling system 80 can utilize oil based on, forinstance, a desired cooling capability, a high specific heat, a highthermal capacity, or a desired viscosity (e. g. for pumping purposes).In another example, cooling oil can also provide for lubrication of thegenerator 14. In the illustrated aspects of the disclosure, thegenerator 14 can be a liquid cooled, dry cavity system having thecooling system 80 illustrated as including the cooling fluid inlet port82 and the shaft outlet port 91 for controlling the supply of thecooling fluid to the cooling system 80.

The cooling system 80 can further include, for example, a cooling fluidreservoir and various cooling passages. The rotatable shaft 40 canprovide one or more flow channels or paths for the main machine rotor52, exciter rotor 62, and PMG rotor 72. In one non-limiting exampleaspect of the cooling system 80, the rotatable shaft 40 can define aninterior 84 to receive a flow of cooling oil (shown as arrows 85), whichcan be further pumped, transported, delivered, or diverted to additionalcooling passages. In another non-limiting aspect of the cooling system80, the arm 24 or segment 26 can include a first cooling passage 100disposed or arranged to carry a flow of cooling oil through the arm 24or segment 26. The first cooling passage 100 can be operably configuredto thermally receive heat generated in rotationally-supportedcomponents, including, but not limited to, the exciter rotor 62 the PMGrotor 72, or a combination thereof, and transfer the heat to the coolingoil for removal. In yet another non-limiting aspect of the coolingsystem 80, the main machine rotor 52 can include a second coolingpassage 102 disposed or arranged to carry a flow of cooling oil throughthe main machine rotor 52. The second cooling passage 102 can beoperably configured to thermally receive heat generated in the mainmachine rotor 52 and transfer the heat to the cooling oil for removal.Heated oil, Residual, unused, or unspent oil can be discharged from therotatable shaft 40 can be provided to an outlet port, such as the rotorshaft oil outlet 88 or the shaft outlet port 91.

Non-limiting aspects of the disclosure can be included wherein the firstor second cooling passages 100, 102 can be radially spaced about therotatable shaft 40. The first or second cooling passages 100, 102 can beradially spaced based on a desired rotational balance, or a set ofdesired heat removal characteristics. For instance, in one non-limitingaspect, the first or second cooling passages 100, 102 can be disposedproximate to respective main machine 50, exciter 60, or PMG 70heat-generating components to ensure reliable thermal coupling.

As shown, non-limiting aspects of the cooling system 80 can furtherinclude a cooling circuit for the set of stator windings 90 of the mainmachine stator 54. For instance, at least one set of stator windings 90can be wound about the main machine stator 54, wherein

A problem with conventional wet or dry cavity generators is thatconventional cooling system have difficulty removing heat generated byat least one of the main machine stator or the set of stator windingsdisposed or located closer to the axial center of the stator. Heatretained proximate to the axial center of the main machine stator or theset of stator windings can result in reduced generator performance oroutput. Unwanted heat can be caused by, for example, stator core lossesdue to hysteresis or eddy currents generated during generatoroperations. In on non-limiting example, conventional generators canaddress this problem by including a low thermal conductive layer (e. g.approximately 0.12 Watts per degree Celsius-meter; “W/mC”) between thestator and stator windings to thermally conduct a small portion of heataway from the stator to the windings, while an external cooling jacketthermally conducts the majority of heat away from the stator. Aconventional external cooling jacket includes coolant passagesencircling at least a portion of the main machine stator, wherein thejacket coolant passages are fluidly coupled with a liquid coolantsource. The liquid coolant traversing the cooling jacket providescooling to ensure desired generator operation, but the addition ofcooling systems increases the costs, complexity, and adds to the weightand size requirements of the generator system.

Aspects of the disclosure provide an alternative solution to addresscooling problem of at least the main machine stator 54, the set ofstator windings 90, or a combination thereof, by using a specializedconfiguration of main machine stator windings 90 including a thirdcooling passage 104 disposed through the windings 90, and configured tocarry a flow of cooling oil through at least a subset of the statorwindings 90. The third cooling passage 104 can be operably configured tothermally receive heat generated in the main machine stator 54 or theset of stator windings 90 and transfer the heat to the cooling oil forremoval. In one non-limiting aspect, a first end of the set of statorwindings or the third cooling passage 104 can be fluidly connected withthe oil flow by, for example, a stator windings coolant inlet housing122 defining an inlet passage 106, connected with the at least subset ofstator windings 90 axially past the stator winding end turns 92. Heatedoil, Residual, unused, or unspent oil can be discharged from the atleast subset of stator windings 90 by way of a stator windings coolantoutlet housing 124 defining an outlet passage 108, which, for example,can also be located axially past the stator winding end turns 92. Thestator windings outlet passage 108 can be further connected with an oiloutlet port for the generator 14, such as the rotor shaft oil outlet 88or the shaft outlet port 91. Aspects of the disclosure can be includedwherein the coolant inlet housing 122 and the coolant outlet housing 124are axially spaced from one another. At least one of the coolant inlethousing 122 or the coolant outlet housing 124 can be of the form of apancake or ring configuration, relative to the axis of rotation 41.

While the set of stator windings 90 are schematically shown, multiplesets of stator windings 90, or multiple sets of stator windings 90 perstator core slot can be included. For instance, in one non-limitingexample, at least two sets of stator windings 90 can be stacked,layered, embedded, installed, or wound about a stator core slots.Non-limiting aspects of the disclosure can also be included wherein atleast a subset of the stator windings 90 can include an external layerof electrically insulating material to electrically isolate the set ofstator windings 90 from another set of stator windings 90 or the mainmachine stator 54 or stator core.

FIG. 6 illustrates a simplified schematic view of an exemplary set ofstator windings 90, in accordance with aspects disclosed herein. Forexample, the set of stator windings 90 can include a conductive windinghaving a fluid channel disposed throughout the length of the windings90. In the illustrated example, the set of stator windings 90 caninclude a substantially square or quadrilateral cross section having aworking liquid or fluid channel 116. Non-limiting aspects of thedisclosure can also be included wherein the set of stator windings 90includes a layer of electrically insulating material 118 external to,and enveloping the set of stator windings 90, to electrically isolatethe set of stator windings 90 from another set of stator windings 90 andthe main machine stator 54, as explained above. While a substantiallysquare cross section is illustrated for the windings 90, any geometricshape, contour, and the like can be utilized in aspects of thedisclosure (e.g. rectangular, circular, trapezoidal, triangular, etc.).Similarly, while a circular fluid channel 116 is illustrated, anygeometric shape, contour, and the like can be utilized in aspects of thedisclosure (e.g. rectangular, circular, trapezoidal, triangular, etc.).

While a substantially rectangular stator winding 90 cross section isillustrated, any geometric cross section can be included in aspects ofthe disclosure, including by not limited to circular, ovate, square, andthe like. Similarly, while only a single working liquid channel 116 isillustrated in the cross-sectional view A-A, aspects of the disclosurecan include a set of fluidly isolated working liquid channels 116 in asingle set of stator windings 90. For example, a single ovate orrectangular cross section of the set of stator windings 90 can includeparallel or dual working liquid channels 116. In one non-limitingexample aspect of the set of stator windings 90, the working liquidchannel 166 can be 1.0 millimeter to 2.0 millimeters in diameter.

FIG. 7 illustrates one non-limiting example aspect of the statorwindings 90 and third cooling passage 104. As shown, at least a subsetof the stator windings 90 includes a first end 126 of the windings 90and an opposing second end 128 of the windings 90. The at least onesubset of the stator windings 90 can pass through or proximate to atleast one of the stator windings inlet housing 122 or coolant outlethousing 124. At least one of the stator windings inlet housing 122 orthe coolant outlet housing 124 can also include a center bore 120 orthrough-hole configured to receive or match the rotatable shaft (notshown). Non-limiting aspects of the disclosure can be included whereinat least one of the stator windings inlet passage 106 or the coolantoutlet passage 108 can be fluidly connected with the rotatable shaftcoolant flow, described herein. In another instance of the non-limitingexample shown, the first end 126 of a subset of stator windings 90 canextend through or proximate to the stator windings inlet housing 122 andthe coolant outlet housing 124, and connect to an electrical terminal orpower output of the generator 14. In a first example, the stator winding90 can be fluidly connected with the stator windings inlet passage 106by, for instance, an aperture 112 to fluidly receive the coolant(illustrated with cross section of the coolant inlet housing 122 removedto schematically show the inlet passage 106 as an arrow, and traversingtoward the main machine stator). In this first example, the statorwinding 90 can pass through the coolant outlet housing 124 via a throughchannel 110 not fluidly connected with the coolant outlet passage 108.

In another example, a different stator winding 90 segment can be fluidlyconnected with the stator windings coolant outlet passage 108 by, forinstance, an aperture 112 to fluidly provide heated coolant from themain machine stator to the coolant outlet passage 108 (again,illustrated with cross section of the coolant outlet housing 124 removedto schematically illustrated the outlet passage 108 as an arrow). Inthis other example, the stator winding 90 can pass through the coolantinlet housing 122 via a through channel 110 not fluidly connected withthe coolant inlet housing 122. As used herein, “heated coolant” canconvey that the coolant is removing or has removed heat from an upstreamcomponent. The coolant inlet passage 106 and coolant outlet passage 108can be further fluidly connected to a coolant circuit or coolantreservoir.

During power-generating operations, the rotation of the rotatable shaft40 relative to the stationary generator 14 components ultimately inducesgenerates current in the main machine stator windings 90, which isfurther provided to a generator power outlet, which it can be suppliedto power or energize a set of electrical loads. Specifically, therotation of the exciter rotor 62 relative to the exciter stator 64, therotation of the PMG rotor 72 relative to the PMG stator 74, and therotation of the main machine rotor 52 relative to the main machinestator 54 will generate heat due to heat losses, copper losses,resistive losses, winding losses, or the like, as the current traversesthe respective resistive windings. In addition to the winding losses,the aforementioned components 52, 54, 62, 64, 72, 74 can generate orretain unwanted heat due to, for example, core losses due to hysteresisor eddy currents, as explained herein. For instance, as explained above,the main machine stator 54 heat can be generated or retained away fromthe axial ends of the stator 54.

The cooling systems 80 can enable or provide dry cavity-based cooling byway of at least the first, second, and third cooling passages 100, 102,104, or a subset thereof, to thermally transfer heat from the heatedcomponents to the cooling liquid, such as cooling oil. In this sense,the heat generated in the respective components can be conductivelytransferred to the cooling liquid (i. e. “hot” liquid) of the coolingsystem 80, which can be forcibly pumped away from the heat-generatingcomponents.

In one non-limiting aspect of the disclosure, at least a subset of theabove-described cooling system 80 can effectively remove, extract, ortransfer over 39 kiloWatts of heat from a generator 14 rated at 150kiloVolt-Amps or higher without encountering heat transfer limits. Inyet another non-limiting aspect of the disclosure, the above-describedconfigurations can be utilized in a generator 14 achieving a powerdensity greater than 7.9 kiloWatts/kilogram.

The aforementioned aspects of the disclosure enable or provide agenerator 14 having increased cooling capabilities over contemporarygenerators. Since aspects of the disclosure significantly increase themain machine stator 54 or set of stator windings 90 cooling capability,as well as the cooling capability of the PMG rotor 72, the exciter rotor62, or a combination thereof, the generator 14 can be designed oroperated without, or free of, additional cooling systems external to thegenerator 14, other than the cooling system 80 described herein. Forexample, aspects of the disclosure can provide for a dry cavitygenerator 14 wherein the system can be designed or operated without, orfree of, at least an external liquid cooling jacket such that the systemprovides cooling greater than or equal to a predetermined level, whereinthe predetermined level is based on an external liquid cooling jacket.Alternatively, or in addition to the aforementioned benefit, theabove-described aspects enable or provide a generator 14 that operate ata higher power density, or generate increased power levels, without aloss in power-generation efficiency due to undesirable heating.

Operating the cooling system 80 to enable or provide increased coolingcapabilities, and thus higher power generation operating capability,further enables or provides for a generator 14 having a higher overallpower density compared with a conventional electrical machine whereinthe exciter and PMG are arranged in series or sequentially along theaxial direction of the rotational axis. When combined (the coplanarexciter 60 and PMG 70, along with the cooling systems 80 describedherein), the generator 14 can have a power density equal to or greaterthan double that of a conventional electric machine. In one non-limitingexample the generator 14 described herein can generate at least 1megawatt of electrical power utilizing the aspects described herein.

Yet another advantage of the above described aspects can includeincreased efficiency with regards to the cooling system. For instance,wet cavity type of cooling is an effective cooling strategy forgenerators, but is less efficient compared with dry cavity coolingdescribed herein. In another non-limiting example, inefficiencies in wetcavity cooling due to the oil interactions with moving components in thecavity cause significant dynamic losses for the generator. Aspects ofthe disclosure can provide a construction of dry cavity generators thatincludes high efficiency cooling and high power density.

In one non-limiting example, a generator employing aspects of thedisclosure can include a power density of 7.9 kiloWatt/kilogram, orgreater than 7.0 kiloWatt/kilogram. Conventional generators wherein theexciter and PMG are sequentially arranged (i.e. not coplanar) caninclude a power density of 3.3 kiloWatt/kilogram.

Aspects of the generator 14 described herein can also be included in amethod of operating the generator 14. For example, the method ofoperating the generator 14 can include rotating the rotatable shaft 40about the rotational axis 41, with the shaft 40 carrying the arm 24extending radially outward from the shaft 40. The arm 24 can beconfigured to rotatably carry at least one of the exciter rotor 62, thepermanent magnet generator rotor 72, or both rotors 62, 72. At least oneof the exciter rotor 62 or the permanent magnet generator rotor 72 ismounted to the arm 24, and are substantially coplanar at a plane 22orthogonal to the rotational axis 41. In one non-limiting aspect of thedisclosure, method can optionally include supplying liquid coolant to acontained cooling passage, such as the first cooling passage 100 of thearm 24 to extract heat from the arm 24. In another non-limiting aspectof the disclosure, the method can include supplying liquid coolant to acontained cooling passage extending through at least one set of statorwindings 90, such as the third cooling passage 104, to extract heat fromthe at least one set of stator windings 90.

The method described is for example purposes only and is not meant tolimit the method in any way as it is understood that the portions of themethod can proceed in a different logical order, additional orintervening portions can be included, or described portions of themethod can be divided into multiple portions, or described portions ofthe method can be omitted without detracting from the described method.

Although the above aspects have been described in terms of a generatorfor a gas turbine engine, the above-described aspects can be used in anyelectric machine to significantly increase the stator or rotorpower-generating or cooling capability. The above-described aspects ofthe disclosure can be well-suited for certain generator applications,such as a two-pole generator (e. g. two stator poles and two rotorpoles) positioned proximate to the turbine engine, and thus creating ahigh temperature and space or volume-limited environment for generatoroperation.

Many other possible aspects and configurations in addition to that shownin the above figures are contemplated by the present disclosure. Forexample, the set of stator windings can include one or more sequentiallyconnected set of stator windings, wherein the set of stator windings areelectrically connected between one another. In another aspect of thedisclosure, it will be understood that the hollow portion of the set ofstator windings, and coolant flow therethrough can also be applied towinding portions of the exciter 60, the PMG 70, the main machine 50, ora combination thereof. Additionally, the design and placement of thevarious components can be rearranged such that a number of differentin-line configurations could be realized. For instance, aspects of thedisclosure can be included wherein the PMG 70 is located radiallyoutward from the exciter 60. In yet another non-limiting aspect, atleast one of the main machine rotor, main machine stator, housing, orrotatable shaft can be manufactured by way of additive manufacturing, orthree-dimensional printing. Additive manufacturing can further beutilized for at least one of the cooling passages.

The aspects described above provider for a variety of benefits includingthat they have higher efficiency, high reliability, less maintenance,all-attitude operation, and lower weight. By attaining increased coolingcapabilities for the dry cavity electric machine free of cooling systemsexternal to the machine other than those described herein, the electricmachine can eliminate the additional the costs, complexity, weight, andsize requirements of the additional cooling systems otherwise needed.The resulting electric machine is lighter, smaller, and has lesscomplexity than conventional dry cavity machines. The resulting electricmachine also has a higher power density due to at least one of a reducedaxial length of the rotatable shaft, increased power generation due toimproved cooling capabilities, or a combination thereof. Such a weightreduction, improved cooling capabilities, or a higher power density isimportant in a turbine engine environment and provides a competitiveadvantage during flight. The reduced complexity can also correspond toreduced maintenance over time, also providing lower operating costs.

To the extent not already described, the different features andstructures of the various aspects can be used in combination with othersas desired. That one feature cannot be illustrated in some of theaspects is not meant to be construed that it cannot be, but is done forbrevity of description. Thus, the various features of the differentaspects can be mixed and matched as desired to form new aspects, whetheror not the new aspects are expressly described.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe disclosure is defined by the claims, and can include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. An electric machine assembly comprising: ahousing; a shaft configured to operably couple with a source ofrotational force and rotate about a rotational axis and having a shaftcooling passage; an arm carried by and extending radially outward fromthe shaft and having a first cooling passage different from the shaftcooling passage; and an exciter rotor and a permanent magnet generatorrotor carried by the arm; wherein the exciter rotor and the permanentmagnet generator rotor are substantially coplanar at a plane orthogonalto the rotational axis.
 2. The electric machine assembly of claim 1wherein the exciter rotor is positioned radially outward from thepermanent magnet generator rotor.
 3. The electric machine assembly ofclaim 1, wherein at least one of a main machine stator, a main machinerotor, the rotatable shaft, or a housing is formed by additivemanufacturing.
 4. The electric machine assembly of claim 1, furthercomprising an exciter stator carried by the housing and positionedproximate to the exciter rotor and a permanent magnet generator statorcarried by the housing and positioned proximate to the permanent magnetgenerator rotor.
 5. The electric machine assembly of claim 1 wherein theexciter rotor and the permanent magnet generator rotor are coplanar at aplane orthogonal to the rotational axis.
 6. The electric machineassembly of claim 1 wherein the exciter rotor and the permanent magnetgenerator rotor at least partially overlap in the axial directionrelative to the rotational axis.
 7. The electric machine assembly ofclaim 1 wherein the electric machine generates at least 1 megawatt ofelectrical power.
 8. The electric machine assembly of claim 1 whereinthe electric machine includes a power density greater than 7kiloWatt/kilogram.
 9. The electric machine assembly of claim 1 whereinthe electric machine is a dry cavity generator.
 10. The electric machineassembly of claim 9 further comprising a contained liquid cooling systemincluding a set of cooling passages for liquid coolant to flow through.11. The electric machine assembly of claim 10 further comprising a mainmachine rotor carried by the shaft and having at least one rotor poleand at least one second cooling passage located proximate to the atleast one rotor pole.
 12. The electric machine assembly of claim 10further comprising a set of stator windings carried by the housing andhaving a third cooling passage extending through the set of statorwindings.
 13. The electric machine assembly of claim 10 wherein theliquid coolant is oil.
 14. A method of operating an electric machine,comprising: rotating a rotatable shaft about a rotational axis, theshaft carrying an arm extending radially outward from the shaft, anexciter rotor, and a permanent magnet generator rotor; and supplyingliquid coolant from a rotatable shaft cooling passage to a firstcontained cooling passage extending through the arm to extract heat fromthe arm; wherein at least one of the exciter rotor or the permanentmagnet generator rotor is mounted to the arm, and wherein the exciterrotor and the permanent magnet generator rotor are substantiallycoplanar at a plane orthogonal to the rotational axis.
 15. The method ofclaim 14 further comprising supplying liquid coolant to a secondcontained cooling passage extending through at least one set of statorwindings mounted proximate to the rotatable shaft to extract heat fromthe at least one set of stator windings.